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There are quite a few animals that have very strong stomachs. Fish have the strongest stomach being able to dissolve metal.
earthworms have a closed circulatory system
The earthworms digestive system is increased in complexity because of the earthworm's segmentation. On each stop or segmentation there is a sphincter and its own digestion going on.
Earthworms
Digestion
Earthworms do not have respiratory systems. They exchange oxygen through their skin.
closed circulatory system
earthworms have a closed circulatory system
closed circulatory system
The digestion system is about 6.5meters long in an average adult male.
Animal
Earthworms don't have spines, so their nerves don't travel through there.